Move v8_use_external_startup_data out of //build/config:feature_flags.

content/app/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/chrome_build.gni")
 
 content_app_sources = [
   "android/app_jni_registrar.cc",
   "android/app_jni_registrar.h",
   "android/child_process_service.cc",
@@ skipping 52 matching lines @@
   content_app_deps += [
     "//mojo/application/public/interfaces",
     "//mojo/environment:chromium",
     "//third_party/mojo/src/mojo/edk/system",
   ]
 }
 
 content_app_extra_configs = [
   "//build/config/compiler:wexit_time_destructors",
   "//content:content_implementation",
+  "//v8:external_startup_data",
 ]
 
 if (!is_multi_dll_chrome) {
   content_app_deps += [ "//content/gpu:gpu_sources" ]
 }
 
 # This includes the app sources for both the browser and child processes.
 source_set("both") {
   # Only the public target should depend on this. All other targets (even
   # internal content ones) should depend on the public one.
@@ skipping 21 matching lines @@
   source_set("child") {
     visibility = [ "//content/public/app:child" ]
 
     sources = content_app_sources
     configs += content_app_extra_configs
     deps = content_app_deps
 
     defines = [ "CHROME_MULTIPLE_DLL_CHILD" ]
   }
 }